1. Field of the Invention
The present invention provides a stabilized pancreas product, useful, for example, as an animal feed additive.
2. Background of the Invention
Animals encounter periods of suboptimal utilization of feed, for example, during periods of change in production, such as the transition from one feed source or ration to a different food source or ration. These changes often result in the poor utilization of dietary nutrients, and result in less efficient production and increased feed costs.
For example, the swine industry recognizes that nutrition and maximal utilization of feed are important as pigs generally grow much faster in proportion to their body weight than larger animals. See Ensminger, Animal Science, 9th Ed. Interstate Publishers, Inc., Danville, Ill. (1991). To promote efficient growth, swine may be fed a high-energy ration which is low in fiber. However, swine differ in the kind and amounts of nutrients needed according to a number of factors including age, function, disease state, nutrient interaction, and environment. See, for example, Hill et al., Tri-State Swine Nutrition Guide, Bull. No. 869–98, The Ohio State Univ., Columbus, Ohio (1998); and National Research Council, Nutrient Requirements of Swine, 10th Ed., Natl. Acad. Press, Washington, D.C. (1998). To meet these different needs, swine producers may formulate the base feed ration from a wide range of ingredients, including, but not limited to, grain concentrates, protein feeds, pasture, dry forages, silages, and downed crops. In addition, supplements may be used to ensure the ration provides the necessary nutritional requirements. Because each of these ingredients vary in availability, price, and amount or quality of nutrients contained, swine producers change feed ration formulations from time to time. For example, a swine producer may follow a complex schedule of different rations based upon the nutritional needs of each stage of the pig's life, the impact of environmental factors on those nutritional needs, and the availability of specific dietary ingredients.
The weaning transition, that period during which pigs are weaned from the sow onto rations, involves some of the most profound nutritional and environmental changes of any life stage. See, e.g., Efird et al., J Anim. Sci. 55:1370 (1982). As a result, growth stasis, commonly referred to as postweaning lag, is frequently observed in weanling pigs. During postweaning lag, pigs may fail to gain, and may even lose, weight. Postweaning lag may cause significant losses in the swine industry where feed costs account for approximately sixty-five to seventy-five percent of total production costs. Swine producers attempt to minimize the period of postweaning lag through the use of specialized food sources and feed supplements, such as plasma and blood-derived protein, milk products, and soy concentrate, to feed weanling pigs in a phase-feeding program. These food sources and supplements are closely tailored to a weanling pig's nutritional needs, and, as such, may significantly increase the cost of the final feed ration. Thus, the weaning period and postweaning lag significantly impact the efficiency and cost of swine production.
Although a large number of environmental stressors may contribute to the duration of the postweaning lag period, predominant factors are believed to be the change in feed form (from sow's milk to ration) and adjustment to new dietary ingredients. See McCracken et al., J Nutr. 125:2838 (1995); and Pierzynowski et al., J. Pediatr. Gastroenterol. Nutr. 16:287 (1993). During the weaning transition, pigs must adapt from a liquid-based diet consisting of sow's milk to a solid-based diet consisting of formulated animal rations. This change in diet and dietary nutrients, which may occur abruptly, often induces significant physiological responses in weanling pigs, including changes in the morphology of the small intestine and exocrine pancreas function, Cera et al., J Anim. Sci. 66:574 (1988); Cera et al., J. Anim. Sci. 68:384 (1990), and quantitative and qualitative changes in exocrine pancreas function, Lindemann et al., J Anim. Sci. 62:1298 (1986).
Physiology and Function of the Pancreas.
The pancreas is a significant accessory organ of digestion which functions as both an endocrine gland and as an exocrine secretory gland. See, e.g., Currie, Structure And Function Of Domestic Animals, Butterworths Pub., Boston, Mass. (1988). Located in the abdominal cavity in the mesentery, the pancreas secretes digestive enzymes which pass through one or more pancreatic ducts to the small intestine. A diverse array of pancreatic enzymes are known, and these enzymes are generally responsible for the hydrolytic processing of dietary nutrients into units capable of being absorbed by the small intestine. The pancreas secretes enzymes capable of processing each of the major nutrient classes—carbohydrates, lipids, and proteins. Examples of enzymes for processing each of these nutrient classes are respectively known as amylases, lipases, and proteases. Levels of pancreatic enzymes quantitatively and qualitatively change throughout the pig's life based upon the amount and composition of a pig's dietary nutrients. Ethridge et al., J Anim. Sci. 58:1396 (1984).
In a non-pathogenic state, the pancreatic acini cells produce inactive forms of these digestive enzymes. Such forms are known as zymogens or proenzymes. Inactive digestive enzymes are sequestered within zymogen granules, and are activated by proteolytic cleavage, primarily by the enzyme trypsin, once they are secreted into the small intestine. The activation of trypsin, in turn, is orchestrated by trypsin inhibitors, present in acinar and ductal secretions, and duodenal enterokinase, an enzyme generally only present in portions of the small intestine. The combined affect of this regulation ensures that pancreatic enzymes are activated only where needed to effect the hydrolytic processing of dietary nutrients.
Pancreatic Function During Periods of Major Production Changes.
Several investigators have documented the development of the digestive capability of young pigs and the affect of a pig's age, weight, and ration on exocrine pancreas function. For example, Pierzynowski et. al., J Pediatr. Gastroenterol Nutr. 16:287 (1993), reported that the maturation of the exocrine pancreas function is more dependant on weaning than age. Initially, the digestive activity of pancreatic enzymes in weanling pigs is decreased as compared to suckling pigs. However, both basal and postprandial levels of amylases, lipases, proteases, and total pancreatic exocrine secretions increased with time in weanling pigs. These changes correlate strongly with changes in the weanling pig's diet but not with age.
Limits of Exogenous Enzyme Therapy.
Some swine producers have turned to exogenous enzymes as feed additives. The investigation and commercial exploitation of these enzymes has only recently become available through the use of advanced recombinant DNA technology and exogenous expression of enzymes in bacterial and other microbial systems. However, there are several factors limiting the usefulness of exogenous enzymes in animal feed.
First, those skilled in the art have long recognized that exogenous enzymes are not needed to aid digestion in healthy animals. For example, Holden et al., Life Cycle Swine Nutrition, PM-489, 17th Rev., Iowa State Univ., Ames, Iowa (2000), states that pigs “produce adequate quantities of digestive enzymes for digestion of the proteins, carbohydrates, and lipids that they are capable of digesting.” Instead, those skilled in the art utilize exogenous enzymes in order to aid digestion of substances that animals are intrinsically incapable of digesting. For example, barley contains β-glucans, or water-soluble carbohydrates, which are poorly digested by the pig, and those skilled in the art have recognized that β-glucanase-containing feed rations can aid in the digestion of barley when it is used as a dietary ingredient.
Second, each exogenous enzyme generally targets only a narrow range of substrates. Thus, use of exogenous enzymes to aid the digestion of a feed ration in general would require the complex mixing of feed ration containing specific combinations enzymatic substrates and exogenous enzymes. Such pairing would require a significant knowledge of available exogenous enzyme preparations, their specific substrate specificities, and the proper feed ration formulation and storage conditions. Swine producers using exogenous enzymes for this purpose therefore would have to make detailed ration formulation choices, thereby increasing production costs.
Third, the efficacy of exogenous enzyme preparations is significantly altered during commercial processing and formulation of the feed ration. Commercial processing of animal feed often includes heating, extruding, and pelleting. Aggressive commercial processing of exogenous enzymes substantially destroys enzyme activity. Moreover, exogenous enzymes generally self degrade or catalyze the degradation of feed ingredients once the feed ration is formulated. Both of these events significantly reduce the time over which an enzyme-containing feed ration may be stored.
In addition, the digestive system itself provides a significant challenge to the use of exogenous enzymes as feed additives. The feed of non-ruminant animals, such as pigs, must pass through the highly acidic confines of the stomach where digestion of proteins is initiated. Chyme from the stomach then passes the pylorus into the lumen of the small intestine. Although still highly acidic, chyme is quickly neutralized and made slightly alkaline. As such, the majority of digestive enzymes have pH optima at or above neutrality. Thus, the intrinsic characteristics of the digestive system itself requires that exogenous enzymes remain stable in highly acidic conditions, yet function optimally in slightly alkaline conditions.
Pancreatin.
Pancreatin is a pancreas-derived product that is prepared by drying and hydrolyzing swine pancreas. See, e.g., U.S. Pat. No. 3,956,483 (“Preparing Pancreatin”). Pancreatin is made of dried, defatted pancreas. It is prepared from fresh or fresh-frozen pancreas. Normally the pancreas glands are minced and comminuted with the duodenum, which is added to activate the proteolytic enzymes or zymogens in the pancreas. Alternatively, proteolytic activity is sometimes established in the pancreatin preparation by the addition of active trypsin. The blend then undergoes activation of the enzymes. Thereafter, the pancreas is degreased and dried, generally by vacuum drying at room temperature.
Pancreatin has been used in the animal industry primarily to treat digestive disturbances. See, e.g., U.S. Pat. No. 5,112,624 (“Prevention of digestive disturbances in herbivores”); see also Russian Patent No. 829,115 (“Gastrointestinal disorder in calves”). Pancreatin also has been proposed as a feed additive. For example, Cortamira et al., Proc. of the 7th Int. Symp. on Digestive Physiology in Pigs, Univ. Alberta, Edmonton, Alberta (1997), investigated the use of 0.01 to 0.03 percent processed pancreatin in swine feed. See also U.S. Pat. No. 2,878,123 (“Use of Proteolytic Enzymes in Poultry Feed”).
Heretofore there has not been a practicable feed additive based on a stabilized pancreas product. For example, U.S. Pat. No. 3,313,705 discloses a low-temperature process for making a lyophilized pancreas-based medicament. See col. 1, lines 65 to 69. However, the process is cumbersome and impractical to replicate on a commercial scale for animal feed. See col. 2, lines 16–51. Additionally, the disclosed product undergoes autolysis under atmospheric conditions and requires special storage procedures (e.g., the use of a dehydrating stopper). See col. 3, lines 27–39.
Therefore, a strong need exists for a practicable stabilized pancreas product that can be used, for example, as a feed additive.